With the advent of the “Industrial Internet of Things” (IIOT), there is a desire to enable the use of the Transmission Control Protocol/Internet Protocol (TCP/IP) suite or other suitable protocols on numerous network-connected devices within industrial process control and automation systems. Supporting these types of network communications in standard industrial process control and automation devices (such as sensors, actuators, and controllers) would allow those devices to act as IIOT devices.
Communications used to support IIOT are often based on Ethernet or wireless technologies. Ethernet technologies typically support star and ring topologies with point-to-point links. However, Ethernet technologies for a shared medium (such as 10Base5 and 10Base2) are not preferred and are almost obsolete at this point. Also, supporting Ethernet in many industrial environments may require significant investment in industrial switches, or every IIOT device could require a built-in switch. Both can result in increased overall system costs. Moreover, wireless technologies are often not accepted for critical control applications.
While the use of Ethernet rings may avoid the requirement for external switches, Ethernet rings are generally not tolerant to multiple device failures. Two faults in the ring can completely break communications in the ring, and the ring can be disturbed whenever a device is inserted into or removed from the ring. As a result, Ethernet rings may be undesirable in industrial process control and automation systems, particularly with critical control applications where more than one fault needs to be safely handled. While TCP/IP can be used on a shared RS485 bus, the slower speeds provided by RS485 may not meet some industrial control needs.